Accelerator Mass Spectrometry for Measurement of Long-Lived Radioisotopes

TLDR

Particle accelerators coupled with magnetic and electrostatic mass analyzers enable measurement of rare isotopes at abundance ratios as low as 10⁻¹²–10⁻¹⁵, and have been applied across earth sciences, anthropology, physics, and may soon serve materials and biological research. By accelerating ions to multi‑MeV energies, all molecular ions are removed, while negative‑ion production eliminates some isobars and high‑energy energy‑loss detection separates remaining atomic isobars. Using this technique, the long‑lived radioisotopes ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, and ¹²⁹I can be quantified in natural samples containing as few as 10⁵ atoms and isotopic abundances down to 10⁻¹⁵.

Abstract

Particle accelerators, such as those built for research in nuclear physics, can also be used together with magnetic and electrostatic mass analyzers to measure rare isotopes at very low abundance ratios. All molecular ions can be eliminated when accelerated to energies of millions of electron volts. Some atomic isobars can be eliminated with the use of negative ions; others can be separated at high energies by measuring their rate of energy loss in a detector. The long-lived radioisotopes 10 Be, 14 C, 26 Al, 36 Cl, and 129 I can now be measured in small natural samples having isotopic abundances in the range 10 -12 to 10 -15 and as few as 10 5 atoms. In the past few years, research applications of accelerator mass spectrometry have been concentrated in the earth sciences (climatology, cosmochemistry, environmental chemistry, geochronology, glaciology, hydrology, igneous petrogenesis, minerals exploration, sedimentology, and volcanology), in anthropology and archeology (radiocarbon dating), and in physics (searches for exotic particles and measurement of half-lives). In addition, accelerator mass spectrometry may become an important tool for the materials and biological sciences.